It is known that a fuel vapor treatment system determines whether a fuel vapor leak from a fuel tank is in an allowable range based on a pressure in the fuel tank which is detected while a pump is driven to decrease or increase the pressure in the fuel tank. For example, in the fuel vapor treatment system shown in JP-2012-2207A, an interior of a fuel tank is depressurized or pressurized by a vane type pump.
The vane type pump has a housing, a rotor rotatably accommodated in the housing, a vane provided to the rotor in such a manner as to radially reciprocate, and a motor driving the rotor. A tip end of the vane is slidably in contact with an inner wall surface of the housing. When foreign matters are introduced into the interior of the pump, or when worn powders of the vane and the housing accumulate in the pump, a clearance between a rotating part (a rotor, a vane) and a stationary parts (housing) is decreased, which may deteriorates a pump performance. If large amount of foreign matters are introduced or if large amount of the worn powders accumulate, it is likely that the rotation of the rotor may be locked. Furthermore, there is a possibility that a secondary wear may be accelerated and an abrasive wear may occur.